Increasingly strict environmental regulations are being promulgated by governmental agencies, including regulations restricting the emission to atmosphere of hazardous hydrocarbon fuel vapors. Such regulations are becoming increasingly common with respect to machines having small engines including both handheld and ground supported machines such as lawnmowers, leaf blowers, weed trimmers, power washers and the like.
To facilitate compliance with these regulations, various fuel vapor control systems and methodologies have been employed. For example, a carbon canister may be employed to receive fuel vapor from a fuel system, such as from a fuel tank, and to collect and hold the fuel vapor prior to it being purged to an intake manifold of the engine for combustion in the engine. During hot soak conditions, such as when a hot engine is shut off or a vehicle engine is exposed to hot ambient conditions for an extended period of time, fuel vapor generation may be sufficient to saturate or overload the fuel vapor canister. Once saturated or overloaded, the vapor canister is no longer effective. Passively purged vapor canisters may vent to the atmosphere excess fuel vapor which results in unacceptably high hydrocarbon fuel vapor emission to the atmosphere.